A type of hydraulic control device is disclosed in JP2009-299573A (hereinafter referred to as Patent reference 1), which includes a pump driven by a rotation of an engine for discharging oil, a valve timing control device actuated by an oil pressure provided by the oil supplied by the pump, and an engine lubricating device configured to lubricate engine parts by the oil supplied by the pump.
The hydraulic control device disclosed in Patent reference 1 includes a valve device that is configured to supply oil to the valve timing control device on a priority basis when the oil pressure applied to the valve timing control device is low by limiting the oil flow amount from the pump to the engine lubricating device. As a result, when the rotational speed of the pump is low, the oil pressure applied to the valve timing control device is secured on the priority basis, thus, the valve timing control device is adequately actuated without having an electric pump for supplementing a performance of the pump.
The valve device of the hydraulic control device disclosed in Patent reference 1 includes a valve component, a retainer, and a space corresponding to each of the valve component and the retainer to slide, the spaces, which leaves a room for improvement from a point of view in reducing size of the valve system or reducing space the hydraulic control device occupies on installment.
FIG. 14 shows a known device considering the above improvement, in which a flow passage area regulation unit is reduced for the purpose of reducing the space the device occupies in the engine. The known hydraulic control device supplies the oil discharged from a pump 101 to a valve timing control device 102 and to a main gallery 108. A first channel 111 connects the pump 101 and the valve timing control device, and a second channel 113 branched from the first channel 111 connects to the main gallery 108. The second channel 113 is provided with a flow passage area regulation unit 103, which controls a dimension of a flow passage area of the second channel 113. The flow passage area regulation unit 103 includes a spool 131 and a biasing member 132. The spool 131 includes a first surface 131d subjected to a pressure and a second surface 131e subjected to the pressure. A surface area of the second surface 131e is smaller compared to that of the first surface 131d. The first surface 131d and the second surface 131e are formed to face each other with the second channel 113 therebetween. The biasing member 132 biases the spool 131 in a direction to close the second channel 113.
With the hydraulic control device of the above configuration, the spool 131 receives a force similar to the oil pressure of the second channel 113 multiplied by an area difference between the first surface 131d subjected to a pressure and the second surface 131e subjected to the pressure and simultaneously receives a biasing force in the direction to close the second channel 113. When the oil pressure in the second channel 113 is small, the spool 131 receives the biasing force of the biasing member 132 predominately, which in turn moves the spool 131 in the direction to close the second channel 113 and reduces the dimension of the flow passage area of the second channel 113. When the oil pressure in the second channel 113 becomes larger, the spool 131 moves against the biasing force of the biasing member 131 in the direction to open the second channel 113 and increases the dimension of the flow passage area of the second channel 113.
In other words, when the oil pressure applied by the oil supplied from the pump 101 is small, the dimension of the flow passage area of the second channel 113 reduces, and when the oil pressure applied by the oil supplied from the pump 101 becomes large, the dimension of the flow passage area of the second channel 113 increases. As can be seen from the above, the flow passage area regulation unit 103 controls the dimension of the flow passage area with the movements of the spool 131 alone. Having an area for the movements of the spool 131 alone, the hydraulic control device with the above configuration is advantageous in reducing the dimension of the flow passage area regulation unit 103.
FIG. 15 is a cross-sectional view taken along a line XV-XV illustrating the spool 131 in a most closed state in which the spool regulates the flow passage area of the second channel 113 to the narrowest state, which is the state similar to the state shown in FIG. 14. The flow passage area of the second channel 113 at this time is an arc area A not closed by the spool 131 out of the area of an opening 133a for a flow passage formed on a valve body 133. The area of the arc area A is determined so as to supply a minimal oil pressure used at the main gallery 108 in a downstream of the flow passage area regulation unit 103.
When the flow passage area is regulated to the narrowest state, a dimension of the arc area A is small. In other words, a slight positional change of the spool 131 affects largely the flow passage dimension of the second channel 113. Even if the tolerance, for example, for the position of the opening 133a for the flow passage or for a dimension of the spool 131 are within the allowable range, errors in sum may result in the dimension of the arc area A to be substantially different from the predetermined dimension. When the dimension of the arc area A is substantially different from the predetermined dimension, a reliability of a pressure control of the hydraulic control device becomes less reliable. Reducing errors in each component by increasing processing accuracy in turn results in a disadvantage of increasing manufacturing cost of the hydraulic control device.
A need thus exists for a hydraulic control device, which is not susceptible to the drawbacks mentioned above.